Frame-based, on-demand spectrum contention source resolution

ABSTRACT

A method and system by which a base station in a Wireless Regional Area Network (WRAN), and more generally a transceiver in a cognitive radio (CR) system, can communicate with other transceivers to fairly share transmission and reception of scheduled use (“occupancy”) of frames on a single channel within a frame-based, on demand spectrum contention system. The method and system disclose how the base station can initiate contentions for an increased share of the frames available in the following superframe of the CR system. The method and system assure fair and efficient access to the transmission channel by a random number based contention process.

RELATED APPLICATION

The present application relates to and claims the benefit of priority toU.S. Provisional Patent Application No. 61/158,855 filed Mar. 10, 2009,which is hereby incorporated by reference in its entirety for allpurposes as if fully set forth herein. The present application isfurther related to U.S. patent application Ser. No. 12/721,357, filedMar. 10, 2010 entitled, “Frame-Based, On-Demand Spectrum ContentionProtocol Specifications; U.S. patent application Ser. No. 12/721,374,filed Mar. 10, 2010 entitled, “Frame-Based, On-Demand SpectrumContention Methodology; U.S. patent application Ser. No. 12/721,387,filed Mar. 10, 2010 entitled, “Frame-Based, On-Demand Spectrum ProtocolVector Messaging; U.S. patent application Ser. No. 12/721,400, filedMar. 10, 2010 entitled, “Frame-Based, On-Demand Spectrum Contention DataFrame Acquisition; and U.S. patent application Ser. No. 12/721,417,filed Mar. 10, 2010 entitled, “Frame-Based, On-Demand SpectrumContention Destination Resolution; which are each hereby incorporated byreference in their entirety for all purposes as if fully set forthherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate, in general, to cognitiveradio networks and more particularly to on-demand spectrum contentionprotocol specifications.

2. Relevant Background

Modern society is increasingly dependent on the radio spectrum. Therapid increase in wireless services and devices such as mobilecommunications, public safety, Wi-Fi, and informational broadcast serveas indisputable examples of how society uses the radio spectrum on aday-to-day basis. Unlicensed transmission bands can play a key role inthe wireless ecosystem. Specifically Television (“TV”) bands aresignificantly underutilized.

Cognitive Radio (“CR”) is an enabling technology that allows unlicensedradio transmitters to operate in the licensed bands at locations whenthat spectrum is temporarily not in use. Based on cognitive radiotechnology the Institute of Electrical and Electronics Engineers(“IEEE”), following a Federal Communication Commission (“FCC”) Notice ofProposed Rulemaking in 2004, has fostered 802.22 as an emerging standardfor Wireless Regional Area Networks (“WRAN”) aiming to providealternative broadband wireless access in, among other places, ruralareas. CR operates on a license-exempt and non-interference basis in theTV band (between 47-910 MHz) without creating harmful interference tothe licensed services, which include, among others, Digital TV (“DTV”)and Part 74 devices (e.g. wireless microphones).

In a typical deployment scenario, multiple WRAN cells, each of whichcomprises a base station (“BS”) and associated customer premiseequipments (“CPE”), may operate in the same vicinity while coexistingwith DTV and Part 74 devices. In order to effectively avoid harmfulinterference to these licensed incumbents, the set of channels on whichthe WRAN cells are allowed to operate could be quite limited. Forexample as shown in FIG. 1, residing within the protection contours ofDTV 140 and wireless microphones 150, both Network 1 110 and Network 3130 are only allowed to operate on channel A, while Network 2 1220 mayoccupy either channel A or B, assuming that in total only 3 channels(channels A, B and C) are available. If WRAN1 and WRAN3 (also referredto herein as Network 1 and Network 2) attempt to perform datatransmissions on channel A simultaneously, mutual interference betweenthese collocated WRAN cells could degrade the system performancesignificantly.

The coexistence (sharing of resources) between incumbent users andsecondary users is referred to as incumbent coexistence, and thecoexistence between WRAN cells is referred to as self-coexistence. Thereare two main objectives in self-coexistence: minimizing theself-interference between co-channel overlapping cells, and satisfyingthe Quality-of-Signal (“QoS”) of the cells' admitted service workloadsin a dynamic spectrum excess environment.

Distributed, cooperative, and real-time spectrum resource sharingprotocol is called On-Demand Spectrum Contention (“ODSC”). The basicmechanism of ODSC is as follows: on an on-demand basis, BSs of thecoexisting WRAN cells contend for the shared spectrum by exchanging andcomparing randomly generated spectrum access priority numbers via MediumAccess Control (“MAC”) layer messaging on an independently accessibleinter-network communication channel. The contention decisions are madeby the coexisting network cells in a distributed way. Only the winnercell, which possesses a higher spectrum access priority compared tothose of the other contending cells (the losers), can occupy the sharedspectrum.

The effectiveness of the ODSC protocol relies on the availability of anefficient and reliable inter-network communication channel for theinteractive MAC message exchanges among network cells. In fact, inaddition to supporting cooperative spectrum sharing protocols such asODSC, a reliable inter-network communication channel is alsoindispensable to other inter-network coordinated functions for 802.22WRAN and, in general, other types of cognitive radio based networks(e.g. inter-network synchronization of quiet periods for spectrumsensing, and coordinated frequency hopping). Beacon-based inter-networkcommunication protocol called Beacon Period Framing (“BPF”) protocol isanother technique used to realize a means for reliable, efficient, andscalable inter-network communication channel sharing by reusing theRadio Frequency (“RF”) channels occupied by the network cells.

ODSC is a coexistence protocol that employs interactive MAC messaging onthe inter-network communication channel to provide efficient, scalable,and fair inter-network spectrum sharing among the coexisting WRAN cells.To achieve these design goals, ODSC allows the coexisting WRAN cells tocompete for the shared spectrum by exchanging and comparing randomlygenerated contention access priority numbers carried in the MACmessages. Such spectrum contention process is iteratively driven byspectrum contention demands (i.e. intra-cell demands for additionalspectrum resources to support data services, and inter-cell demandsrequesting for spectrum acquisitions). The contention decisions are madeby the coexisting network cells in a distributed way, which allows anarbitrary number of cells to contend for the shared spectrum in theproximities without relying on a central arbiter. Instead of behavingselfishly, the competing cells cooperate with one another to achieve thegoals of fair spectrum sharing and efficient spectrum utilization.

Currently, before initiating MAC layer messaging of the ODSC protocol, aWRAN cell that is demanding additional spectrum resource first evaluatesand selects a channel on which no incumbent is detected. The cell thenverifies whether the selected channel can be shared, employing thetransmit power control (“TPC”) technique, with all other co-channelcommunication systems in the neighborhood. If it is feasible, the WRANcell schedules its data transmissions on the selected channels withappropriate TPC settings. Otherwise, ODSC messaging takes place allowingcooperative spectrum contention among WRAN cells to share the targetchannel in a time-sharing manner.

As can be appreciated by one skilled in the relevant art, overlapping(one-hop) cells must compete for the use of the same spectrum in orderto minimize or eliminate mutual interference that may render both cellsunreliable. As described in commonly assigned U.S. patent applicationSer. No. 12/354,606 entitled, “On-Demand Spectrum Contention forInter-Cell Spectrum Sharing in Cognitive Radio Networks”, upon capturingthe use of a particular channel, the occupying WRAN cell, referred to asthe ODSC destination (“DST”), announces the occupancy to other cellswithin one-hop using an ODSC announcement message (“ODSC_ANN”). Otherspectrum-demanding WRAN cells, referred to individually as ODSC source(“SRC”), receives the ODSC announcement messages that are regularlybroadcasted by the DST cells. If a SRC receives ODSC_ANN messages frommultiple DSTs, it randomly selects one of the DSTs. Thereafter the SRCdecodes the message from the selected DST and then sends an ODSC requestmessage (“ODSC_REQ”) that it is seeking access to the channel occupiedby the selected DST. The request message includes a spectrum accesspriority number (“SAPN”), which is either a floating point numberuniformly selected from [0, 1] or a fixed point number uniformlyselected from [0, 2^(x)−1] (wherein x is the number of binary bitsrepresenting the fixed point number). Each DST maintains an ODSC_REQwindow so as to allow multiple SRCs to submit ODSC_REQ messages atdifferent time instances without losing its own fair chance toparticipate in the contention process. At the end of an ODSC_REQ window,if any ODSC_REQs are received, the DST randomly generates its own SAPNand compares it with the smallest SAPN carried in the received ODSC_REQmessages. When the DST's SAPN is smaller (i.e. possesses higherpriority), DST sends each SRC an ODSC response message (“ODSC_RSP”)indicating a contention failure. Otherwise, the SRC with the smallestSAPN will receive an ODSC_RSP with an indication of contention successmeaning that access and control of the spectrum resource (channel) willbe relinquished by the DST in favor of the winning SRC. The DST alsosends a message to the other SRCs informing the SRCs of a contentionfailure. As one skilled in the art will recognize other criteria may beused to determine SAPN priority. For example, the contention participantpossessing the largest SAPN may win the contention in another embodimentof the invention.

Upon receiving a success notice, the winner SRC broadcasts an ODSCacknowledgement (“ODSC_ACK”) indicating the time, Tacq, at which itintends to acquire the channel from the selected DST. All DSTs that areon the same channel as the one being contended for and are within aone-hop distance of the winner SRC respond to the ODSC_ACK by schedulinga channel release to occur at Tacq and broadcast an ODSC release message(“ODSC_REL”) to the neighborhood. The ODSC_REL contains informationabout the channel to release, the channel release time (set to Tacq),and the identification of the winner SRC that will acquire the channel.If the ODSC_ACKs are received from multiple SRCs before the channel isreleased, a DST selects the earliest Tacq specified in the receivedODSC_ACK as the channel release time. This avoids collisions between theneighboring DST and SRC when the channel switching times do not agree.All SRCs that capture the ODSC_REL will also schedule channelacquisitions at Tacq as long as it is determined from the ODSC_REL thatthe one-hop DST is releasing the channel to either itself or to a winnerSRC that is multiple hops away. On the other hand, if multiple ODSC_RELswith different Tacq are received before the channel switching, theearliest Tacq is taken for channel acquisition.

In a large scale network, it is likely that multiple DSTs and multipleSRCs coexist. As the contention processes are fully random andindependent, different SRCs could select their own DSTs to contend forthe same spectrum resource and the contention outcomes (i.e. winners ofthe contention and channel acquisition/release times) could be inconflict. The ODSC message flow described above is designed tocoordinate the discrepancies between the conflicting contentiondecisions in order to ensure the stability of the coexistence behaviorsand avoid loss of spectrum efficiency across the networks. However, atany one time only one network cell can utilize the shared channel inclose proximity. While the network cell occupying the channel sends andreceives data over a particular period of time, other neighboringnetwork cells remain idle. This is true even when the network celloccupying the channel may not be fully utilizing the bandwidth of thechannel over its allocated period of time. Additionally a network celldemanding a spectrum resource would have to remain idle for a relativelylong duration (in the order of plurality of frames) until the channel toshare is released by the occupying network cell. As a consequence, sucha potentially long turnaround time of channel acquisition may negativelyimpact the quality of service (“QoS”) of time sensitive applications dueto the long service interruptions. Spectrum sharing on a finergranularity than a channel (such as frame-based) is advantageous toenhance both the utilization of the operating spectrum and the QoS ofthe application.

What is needed is a set of general mechanisms for an arbitrary number ofdistributed network devices to share limited spectrum resources.Although the above description of the ODSC protocol outlines how aprotocol is employed for resolving problems of radio resource sharingwhere the basic unit of the spectrum resource is a radio frequencychannel, the same principal of ODSC applicability, without loss ofgenerality, is desirable to other, more fine grained, apportionment ofthe shared spectrum. It is desirable to apportion the shared radiospectrum so that any effective combination of radio spectrum resource inboth the time and frequency domain, such as a frame on a frequencychannel or multiple frames on multiple frequency channels, can beeffectively shared.

The present invention addresses a mechanism and special features of theODSC protocol of spectrum sharing on a frame-by-frame basis. Thisprotocol is referred to hereafter as frame-based, on-demand spectrumcontention. These and other improvements to the prior art are addressedby one or more features of the present invention.

SUMMARY OF THE INVENTION

A frame-based, on-demand spectrum contention protocol provides finegrained allocation of a limited spectrum resource. In a CR system,determination of spectrum resource allocation is accomplished on aframe-by-frame basis over a predetermined interval of frames. Accordingto one embodiment, a superframe comprising 16 data frames can beapportioned for use among a plurality of overlapping network cells suchas WRAN cells so as to better and more equitably distribute a sharedspectrum resource.

For a predetermined period of time, a WRAN cell, occupying one or moredata frames of a superframe, senses whether other WRAN cells within onehop are seeking access to same occupied frames. Likewise a WRAN cellseeking additional spectrum resources can examine the CR networktopology to determine to which WRAN cell a request for additionalresources should be sent.

After a WRAN cell occupying a particular frame (the target frame)receives one or more external demands for access to the target frame ofa superframe (the occupying cell can also vie to maintain control of thetarget frame), a contention is declared. (Note: in the operatingenvironment, the WRAN cell does not possess any preferential right to atarget frame) A WRAN cell initiating access demand and sending acontention request for the target frame is called a contention source.The WRAN cell currently occupying the target frame and receiving thecontention request(s) from one or more contention source is called acontention destination. Each request includes a spectrum contentionnumber generated, according to one embodiment of the present invention,based on a random process. Upon receiving the requests and the spectrumcontention number from a neighboring contention source, the contentiondestination cell currently occupying the targeted frame generates itsown spectrum contention number and compares all of the generatedspectrum contention numbers (including numbers generated by thedestination cell and those numbers received from a contention source) todetermine a winner.

According to one embodiment of the present invention, the smallestspectrum contention number of the cells vying for access to the sharedspectrum resource will win the contention. A winner is declared and anannouncement is broadcast to all cells within one hop of the contentiondestination of the targeted frame, indicating the winner of the targetedframe. The winning cell will, at the end of a certain period, (normallythe superframe) thereafter occupy the targeted frame. Upon receiving thebroadcast message announcing the winner, the winning cell, if differentthan the current occupier of the targeted frame, broadcasts to all ofits one hop neighbors of impending occupancy of a targeted frame. Thus,networks cells that may not be within one hop of the releasing cell willnonetheless be notified of the impending occupancy of a targeted frameby the winning cell.

According to one embodiment of the present invention, communication ofcontrol messages for frame-based, on-demand spectrum contention (forexample frame occupancy requests) are wirelessly conveyed during abeacon frame window attached to the trailing edge of each data frame.Over the span of a 16 frame superframe, 16 beacon frame windows areavailable to provide information throughout the CR network of frameallocation. For example, frames 1 though 4 can be used for sensingcontention requests. The contention resolution can occur during frames 5and 6 with a response broadcast on frame 7. Acknowledgements by thewinning frames can be broadcast on frame 8 with a release of the framebroadcast on frame 16.

Other informational communication schemes operable to conveysynchronization and frame allocation data amongst a plurality of cellsare equally applicable to the various embodiments of the presentinvention as are the factors used to determine which cell in thecontention process will gain access to the contended spectrum resource.

The features and advantages described in this disclosure and in thefollowing detailed description are not all-inclusive. Many additionalfeatures and advantages will be apparent to one of ordinary skill in therelevant art in view of the drawings, specification, and claims hereof.Moreover, it should be noted that the language used in the specificationhas been principally selected for readability and instructional purposesand may not have been selected to delineate or circumscribe theinventive subject matter; reference to the claims is necessary todetermine such inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other features and objects of the presentinvention and the manner of attaining them will become more apparent,and the invention itself will be best understood, by reference to thefollowing description of one or more embodiments taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 shows an exemplary overlapping network configuration of a TVwireless system employing cognitive radios as would be known to one ofreasonable skill in the relevant art;

FIG. 2 is a high level block diagram depiction of a superframe structureutilized in a frame-based, on-demand spectrum contention protocolaccording to one embodiment of the present invention;

FIG. 3 is a top level flowchart for an inter-WRAM coexistence procedureemploying frame-based, on-demand spectrum contention protocols accordingto one embodiment of the present invention;

FIG. 4 is a graphical depiction of a typical message flow carried outvia beacon windows of the frame-based, on-demand spectrum contentionprotocol according to one embodiment of the present invention;

FIG. 5 shows a flowchart of an overall procedure for frame-based,on-demand spectrum contention according to one embodiment of the presentinvention;

FIG. 6 depicts a high level flowchart of one method embodiment of thepresent invention for determining the availability of data frames in anframe-based, on-demand spectrum contention environment;

FIG. 7 is a flowchart of one embodiment of the present invention forframe acquisition in a frame-based, on-demand spectrum contentionenvironment;

FIG. 8 is a flowchart of a procedure for a frame-based, on-demand sourcespectrum contention (as executed by a spectrum contention source)according to one embodiment of the present invention;

FIG. 9 is a flowchart of a procedure for a frame-based, on-demanddestination spectrum contention (as executed by a spectrum contentiondestination) according to one embodiment of the present invention;

FIG. 10 is a high level flowchart of message generation at a spectrumcontention destination involving multiple frames and multiple spectrumcontention sources, according to one embodiment of the presentinvention;

FIG. 11 is a high level flowchart of the release of pending operationsat a contention destination, according to one embodiment of the presentinvention;

FIG. 12 is a graphical depiction of three overlapping WRAN networks andtheir respective communication paths used for evaluation of aframe-based, on-demand spectrum contention protocol; and

FIG. 13 is an overlapping wireless CR network configuration of aplurality of overlapping base stations implementing a frame-based,on-demand spectrum contention resolution protocol according to oneembodiment of the present invention.

The Figures depict embodiments of the present invention for purposes ofillustration only. One skilled in the art will readily recognize fromthe following discussion that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles of the invention described herein.

GLOSSARY AND ACRONYMS

As a convenience in describing the invention herein, the followingglossary of terms is provided. Because of the introductory and summarynature of this glossary, these terms must also be interpreted moreprecisely by the context of the Detailed Description in which they arediscussed.

Spectrum Contention Source (“SC-SRC”)—the WRAN cell that is demandingadditional spectrum resources (i.e. data frames transmissionopportunities on a TV channel) and is initiating an interactive spectrumcontention process with the target Spectrum Contention Destination.

Spectrum Contention Destination (“SC-DST”)—a WRAN cell that is thetarget of the spectrum contention request initiated by the SC-SRC, andis the occupier of the spectrum resources being requested to be sharedwith the SC-SRC.

Spectrum Contention Number (“SCN”)—the contention number randomlygenerated by SC-SRCs and SC-DSTs for determining the priority ofspectrum access.

Spectrum Contention Request (“SC-REQ”)—This is a unicast request messagetransmitted by the SR-SRC for initiating the spectrum contentionprocess.

Spectrum Contention Response (“SC-RSP”)—This is a unicast responsemessage transmitted by the SC-DST responding to the requesting SC-SRCwith regard to the contention results.

Spectrum Contention Acknowledge (“SC-ACK”)—A broadcast acknowledgementmessage transmitted by the winner SC-SRC indicating the confirmation ofspectrum acquisitions.

Spectrum Contention Release (“SC-REL”)—A broadcast message transmittedby the granting SC-DST indicating the announcement of the spectrumreleases.

Target Frame—a particular frame in a superframe which is the focus of acontention process between two or more overlapping network cells.

DESCRIPTION OF THE INVENTION

Embodiments of the present invention are hereafter described in detailwith reference to the accompanying Figures. Although the invention hasbeen described and illustrated with a certain degree of particularity,it is understood that the present disclosure has been made only by wayof example and that numerous changes in the combination and arrangementof parts can be resorted to by those skilled in the art withoutdeparting from the spirit and scope of the invention.

A frame-based, on-demand spectrum contention protocol enables dynamicspectrum sharing for coexistence operations among a plurality ofoverlapping wireless network cells. As previously described, wirelesscells in a CR communication system contend for the use of sharedresources. As a means to efficiently and effectively utilize theavailable communication spectrum, CR systems initiate a competitiveprocess where each system contends for the use of the same resource.

As is well known to one of ordinary skill in the relevant art, wirelesscommunication between a base station (“BS”) and one or more ConsumerPremise Equipment (“CPE”) within its area of influence is accomplishedvia one or more channels. As discussed, in commonly assigned U.S. patentapplication Ser. No. 12/354,606, entitled “On-Demand Spectrum Contentionfor Inter-Cell Spectrum Sharing in Cognitive Radio Networks” aninteractive message exchange can be undertaken to resolve contentionsfor the use of a particular channel. In such situations, using the ODSCprotocol, a plurality of base stations in coexisting (overlapping) WRANcells contend for the use of a particular channel of a shared spectrum.As a result of the contention process, a single base station gainscomplete access to a particular channel until another contention for theshared spectrum is raised.

During the period of time in which the winning base station has use ofthe channel, other coexisting base stations are precluded fromcommunicating. The present invention provides a message-based, demanddriven, distributed spectrum sharing protocol for use in contentionbased CR communication systems. Rather then resolving shared spectrumresource contentions on a coarse-grain, channel-by-channel basis, thepresent invention enables a fine-grain, frame based, resolution ofshared spectrum contentions. While the embodiments of the presentinvention are largely described with regard to wireless regional areanetworks, one of reasonable skill in the art will understand that theconcepts presented herein are equally applicable to any wireless networkand cognitive radio communication system.

According to one or more embodiments of the present invention, messagesare exchanged between base stations contending for a commonly sharedresource to determine their respective rights to that resource. Whilethe present invention is primarily described with reference to thecoexistence contention process for a shared resource associated with asingle channel, one of ordinary skill in the relevant art will recognizethat the same contention protocol is equally applicable to contentionsinvolving multiple frames among multiple channels or generally afractional combination of channels in both the time and frequencydomain. Indeed a likely implementation of the present invention involvesthe resolution of contentions from a plurality of base stations over aplurality of shared resources associated with a plurality of channelsinvolving multiple frames in both the time and frequency domain. Thepresent invention contemplates the protocols presented herein arescalable to any CR communication system regardless of size.

By using random spectrum contention numbers generated by each basestation, the present invention provides a fair and robust means forshared spectrum contention resolution with low computational overheadand high quality-of-signal results.

Unlike the traditional contention based medium access schemes such asAloha and Carries Sense Multiple Access (“CSMA”), ODSC protocol, asdescribed above, takes distinguishable approaches for resolving channelaccess contention and mitigating access collision, aiming to improve thespectrum access efficiency. Due to the lack of exact knowledge of whenthe neighboring systems will transmit, a wireless system using Aloha orCSMA protocol generally resolves the access contention by deferring datatransmission for a random period, and in the case of collision,re-initiates the contention process by setting a potentially much largerrandom period for the transmission deferral (e.g. using the exponentialrandom back-off mechanism) in order to reduce the chance of reoccurringcollisions.

A better approach and according to one embodiment of the presentinvention, ODSC allows a wireless system (IEEE 802.22 WRAN in thepresent case) to compete for the channel access without resorting to anytransmission deferral which clearly sacrifices the spectrum efficiency.This is because the contention resolution process is carried out inparallel with the on-going data services. Moreover, as the spectrumcontention is resolved by comparing the spectrum access priority numbersthat are randomly selected from a very large pool of values, thelikelihood of access collision among coexisting wireless systems usingODSC is effectively minimized.

One facet of the present invention is its frame-by-frame contentionresolution within each channel's superframe. FIG. 2 is a graphicaldepiction of a frame-based, on-demand ODSC communication system. In theCR communication system shown in FIG. 2, three BSs as originallydepicted in FIG. 1 contend for the communication resources available inchannel A. Data conveyed on channel A is packaged into discrete framesand superframes. In this particular embodiment, a superframe iscomprised of 16 frames. In other implementations, the number of frameswithin a superframe may vary and indeed the entire concept of asuperframe with respect to its relationship to individual data frames orpackets may vary without departing from the scope and intent of thepresent invention.

Each line shown in FIG. 2 represents frame allocation to a BS definednetwork. Network 1 210 as shown in FIG. 1 is the top line while Network2 220 is the second line and Network 3 230 is the bottom line. As shownin FIG. 1, Network 2 220 overlaps with Network 1 210 and Network 3 230.Network 1 210 however is independent of Network 3 230. Thus the samespectrum resources can be used simultaneously by Network 1 210 andNetwork 3 230. The contention for the available spectrum resource ofchannel A is therefore between Network 2 220 and Networks 1 and 3 210,230.

A superframe 240, 250 includes, according to one embodiment of thepresent invention, 16 individual data frames 240 ₀₋₁₅, 250 ₀₋₁₅. Eachdata frame 240 ₀₋₁₅, 250 ₀₋₁₅ is separated by a beacon window 260. Eachdata frame 240 ₀₋₁₅, 250 ₀₋₁₅ and each beacon window 260 are timepartitioned and fixed in size. And, as can be seen in FIG. 2, thesuperframes of each network 210, 220, 230 are, in this example,synchronized. In other embodiments of the present inventionsynchronization is not required.

The beacon window 260 (also referred to herein as a beacon period orbeacon period frame) allows coexisting WRAN cells such as Network 1 210and Network 2 220, and Network 2 220 and Network 3 230 to exchangecoexistence beacons for inter-network communication. Other inter-networkcommunication protocols and systems can be used without detrimentallyimpacting the unique and non-obvious features of the present invention.The ability for contending networks to communicate resource needs and tocommunicate resource management allocations is a fundamental aspect ofthe present invention.

These and other implementation methodologies for inter-networkcommunication can be successfully utilized by the frame-based, on-demandspectrum contention protocol. These implementation methodologies areknown within the art and the specifics of their application within thecontext of the present invention will be readily apparent to one ofordinary skill in the relevant art in light of this specification. Forexample inter-cell communication can be accomplished using a dedicatedcommunication channel, one or more dedicated communication frames withinthe superframe, back channels, a wired interface such as Ethernet orother wired communications systems, or any other means by which two ormore base stations can convey spectrum resource allocation information.Moreover the timing of the communication is flexible and can be adjustedto meet the needs of the network without detrimentally altering theefficiency and success of the present invention.

FIG. 3 is a top level flowchart showing inter-WRAN coexistenceprocedures. In the following description it will be understood that eachblock of the flowchart illustrations, and combinations of blocks in theflowchart illustrations, that follow can be implemented by computerprogram instructions. These computer program instructions may be loadedonto a computer or other programmable apparatus to produce a machinesuch that the instructions that execute on the computer or otherprogrammable apparatus create means for implementing the functionsspecified in the flowchart block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable apparatus to function in aparticular manner such that the instructions stored in thecomputer-readable memory produce an article of manufacture includinginstruction means that implement the function specified in the flowchartblock or blocks. The computer program instructions may also be loadedonto a computer or other programmable apparatus to cause a series ofoperational steps to be performed in the computer or on the otherprogrammable apparatus to produce a computer implemented process suchthat the instructions that execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

Accordingly, blocks of the flowchart illustrations support combinationsof means for performing the specified functions and combinations ofsteps for performing the specified functions. It will also be understoodthat each block of the flowchart illustrations, and combinations ofblocks in the flowchart illustrations, can be implemented by specialpurpose hardware-based computer systems that perform the specifiedfunctions or steps, or combinations of special purpose hardware andcomputer instructions.

As a BS is powered on 310 it begins a BS Network discovery process 320.Other BS within its range of operation are identified directly and bycommunicating with CPEs within its area of coverage other overlappingnetwork cells can be identified. During this period of discovery, eachBS identifies TV channel occupancies of neighboring WRAN cells andself-coexistence window reservations of the neighboring WRAN cells.Finally, individual frame reservation patterns (as described hereafter)of each neighboring WRAN cell on specific TV channels are determined.Based on its network discovery, the BS undergoes an etiquette-basedchannel acquisition 330 which is to identify and acquire an available TVchannel without detrimentally affecting incumbent device operation andneighboring WRAN cells. For example based on the TV channel occupancy byincumbent devices and available channel spectrum resources, a new BS maydetermine that it should operate on channel A along with any otheroverlapping base stations. Thus, the new BS may have to contend for alimited shared spectrum resource.

Upon choosing one or more channels on which to operate, a base stationattempts to acquire 340 exclusive use of that (those) channel(s). To doso, a request is sent out by the base station to determine whether anyother base stations are currently using the channel. When no response tothe request is received, the requesting BS issues an announcement of itsuse and effective ownership of the channel. Shortly thereafter, the BScan use the channel for normal data services 360.

A more frequent response to the base station's attempt to acquireexclusive use of a channel is a denial indicating that another basestation or stations are currently using that spectrum for data services.According to one embodiment of the present invention the requesting basestation enters an inter-WRAN frame-based, on-demand spectrum contentionprocess 350 for co-channel sharing. (explained in detail below withreference to subsequent figures). Upon successful resolution of thatprocess the base station gains access to at least a portion of thespectrum and begins normal data services 360.

While the base station utilizes the spectrum for data services, otherdemands or requests for the shared spectrum may arise. These requests ordemands may be externally or internally generated. An external demandfor inter-WRAN spectrum sharing 370 may arise from another BS joiningthe network or an existing BS in the network seeking additional spectrumresources. Another external demand may be an increased utilization ofthe spectrum by the incumbent (TV) resulting in a reduction in overallspectrum availability. Similarly, an internal demand for spectrumacquisition 380 may arise from a base station's realization that itsallocated shared spectrum is insufficient to meet its data servicesrequirements. For example, CPEs within its own cell may demandadditional spectrum resources. Thus, the BS internally issues a demandfor additional spectrum resources.

When a BS realizes that it possesses an internal demand for additionalspectrum resources 380, it again initiates an etiquette-based channelacquisition procedure 330. The base station hence reexamines thespectrum to determine if it can acquire another channel. If the channelis acquired, the BS begins normal data services 360 and thereafterdetermines whether it now possesses enough of the spectrum to meet itsinternal needs. If an additional (or different) channel is not acquiredthen it returns to, and reinitiates an inter-WRAN frame-based spectrumcontention in hopes to gain more of the existing shared spectrum.

If an external demand for inter-WRAN spectrum sharing 370 is receivedeach participating BS (WRAN) again competes for a portion of the sharedresources. By continually evaluating the allocation of shared resources,each WRAN gains an equal share of the shared resource. FIG. 2 shows arepresentation of frame-based, on-demand spectrum contention allocation.Shown are frames associated with two superframes that are allocatedamong three overlapping WRAN cells.

Referring again to FIG. 2, each superframe 240, 250 of a shared channelcomprises 16 data frames 240 ₀₋₁₅, 250 ₀₋₁₅. In the first superframe 240the first 3 data frames of channel A 240 ₀, 240 ₁, 240 ₂ are beingutilized by Network 1 210 and Network 3 230 without contention. Recallthat Network 1 210 and Network 3 230 do not overlap. During this timeperiod frames 0-3, Network 2 is unable to transmit or receive data andis thus idle.

In the second superframe 250, Network 2 220 occupies the initial dataframe 250 ₀ to the exclusion of Network 1 210 and Network 3 230. Thus,for frame 250 ₀ Networks 1 210 and 3 230 are idle. In this manner eachof the three Networks 210, 220, 230 can be provided shared access to thelimited spectrum resource increasing the overall quality-of-signal ineach network.

FIG. 2 additionally depicts the presence of a beacon window 260following each data frame 240, 250. Upon the initiation of an inter-WRANframe-based ODSC these beacon windows are used to carry request,response or acknowledgement messages between the participating WRANcells.

FIG. 4 is a graphical depiction of a typical message flow carried outvia beacon windows of the frame-based, on-demand spectrum contentionprotocol according to one embodiment of the present invention. In thescenario shown in FIG. 4, three WRAN cells are contending for a sharedframe resource. Returning again to the communication network shown inFIG. 2, assume that during an initial etiquette-based channelacquisition process, Network 2 220 acquired sole use of channel A.Shortly thereafter, Network 1 210 and Network 3 230 joined thecommunication network with their cells overlapping as shown. The messageflow in FIG. 4 is an example of Network 1 210 and Network 3 230attempting to gain shared access to the spectrum currently controlled byNetwork 2 220.

SC-SRC is a designation placed on those cells that serve as the sourceof contention. In this case two WRAN BSs, Network 1 210 and Network 3230, are seeking additional spectrum resources and are thus designatedas a spectrum contention source 420 or SC-SRC. Similarly, the WRAN cellthat currently is in control of a spectrum resource is designated as thedestination to which the contention is directed or SC-DST 410. As one ofreasonable skill in the relevant art will recognize, the title of SC-DSTand SC-SRC is solely based on which cell currently controls or seeks aparticular shared spectrum resource. As the allocation of the sharedresource changes, so too will the respective labels. And, indeed, aparticular cell can for one portion of the spectrum be a destination,meaning it currently controls the spectrum, while at the same time be asource for a contention request as it seeks additional spectrumresources for data services.

Turning attention back to FIG. 4, each contention source, SC-SRC issuesseparate spectrum contention requests 425 for additional sharedresources. Note that the requests for additional resources can be issuedat different times but, nonetheless, must be within a certain window soas to be accepted for consideration. According to one embodiment of thepresent invention, each SC-REQ includes a spectrum contention numbergenerated by the SC-SRC. As will be described later, the spectrumcontention number is a number used by the SC-DST to determine resourceallocation. Upon receipt of a request or requests, the cell which iscurrently in control of the resource, SC-DST, undergoes a spectrumcontention analysis using the gained various spectrum contentionnumbers.

In addition to the source cells requesting access to the sharedresource, the destination may also participate in the contention. Thus,in the present example, three cells are competing for the same sharedresource. Recall that this contention is taking place on aframe-by-frame basis. As the contention analysis takes place, thedestination cell maintains control and use of the shared resource. Whilethe entire contention process may occur over the length of a singleframe, other embodiments of the present invention, a predeterminedperiod of time, can be specified giving the SC-DST a time period ofknown data frames. For example, assume that a contention for a sharedresource has been received and that evaluation of the contentionalgorithms takes place over 3 frames. During those 3 frames the SC-DSTcan prioritize data services knowing that the allocation of the spectrummay soon be diminished. Typically, the contention process is conductedand completed within the time period elapsed during a superframe or, inone embodiment, 16 data frames. However, the resolution of a contentioncan be arbitrarily set based on the needs of the CR communicationnetwork.

Upon completion of the contention process, the SC-DST will determinewhich network cell, in this case Network 1 210, Network 2 220 or Network3 230 will gain (or maintain) control of the shared resource. Accordingto one embodiment of the present invention, each destination cell knowsof the topology of its one-hop neighbors. Thus, in this example, Network2 220 is aware that while both Network 1 210 and Network 3 230 arewithin one hop of Network 2 220, Network 1 210 and Network 3 230 canoperate autonomously. Thus, if either Network 1 210 or Network 3 230wins the contention, the other cell can also use the shared resource.

As shown in FIG. 4, the destination cell, SC-DST, broadcasts a response430 providing the results of the inter-WRAN frame-based spectrumcontention to each of its one-hop neighbors in the form of a SC-RSPmessage. Each cell receiving the message responds with a similarbroadcast acknowledgement message 440 (SC-ACK) stating whether or not ithas received access to the shared resource.

Assume in this case that Network 1 210 had won the inter-WRANframe-based spectrum contention. The SC-RSP message 430 broadcast fromNetwork 2 220 would indicate that Network 1 210 won the contention.Included in the message, according to one embodiment of the presentinvention, would be a proposed release time of the resource. The messagemay also include that Network 3 230 will also have use of the sharedspectrum as Network 1 210 and Network 3 230 do not coexist.

The broadcast acknowledgement message 440 from each SC-SRC (Networks 1210 and 3 230) inform its one-hop neighbors of its impending use (ornon-use) of a particular shared resource. In this case both Network 1210 and Network 3 230 would be informing all of their one-hop neighborsthat they are about to gain control of a particular frame-based sharedresource.

Once the acknowledgement message 440 has been sent, the SC-DST (Network2 220) issues a release (SC-REL) 450 relinquishing control of the sharedspectrum resource. At that point Network 1 210 and Network 3 230 changetheir designations from contention source, to contention destination.Likewise, Network 2 220, with respect to this shared spectrum resource,can issue a spectrum contention request making it a spectrum contentionsource. Assuming that a single message can take place during any onebeacon window 260, the entire contention, response, acknowledgement andrelease can occur in as little as 4 frames of a superframe.

The present invention discloses a frame-based, on-demand inter-WRANspectrum contention protocol. The fine-grained nature of the sharedspectrum contention process can place a single WRAN acting as both acontention source and as a contention destination within a singlesuperframe on any given channel. Indeed, such a contention resolutionscheme could play out for each frame within each superframe.

In the above scenario, Network 1 210 and Network 3 230 are seen ashaving identical allocations to the shared spectrum resource. One ofreasonable skill in the relevant art will recognize, however, that theexample presented herein is a simplified version of what is undoubtedlya more complicated scenario. The above scenario assumes that no otherone-hop neighbors of Network 1 210 and Network 3 230 that are notaffiliated with Network 2 220 have been operating on the same sharedresource. For example, it is entirely possible that while Network 1 210,the winner of the contention with Network 2 220 and Network 3 230, maybe able to gain operational control of a shared resource, Network 3 230may have another coexistence network, Network 4 (not shown) that is alsooperating on, and contending for, the same frame of the same channel Inthat inter-WRAN frame-based spectrum contention, Network 4 may havemaintained control of the shared resource such that upon release byNetwork 2 220, only Network 1 210 and not Network 3 230 may be able toutilize the shared resource.

As previously described, the WRAN BS in control of a spectrum resourcedetermines the winner of contention over that resource. In doing so, thebase station gathers spectrum contention numbers from each participatingWRAN cell and evaluates the values based on, in one embodiment of thepresent invention, a spectrum contention algorithm.

According to one embodiment of the present invention, the spectrumcontention algorithm is of the form:

Spectrum Contention ( N, WRAN, SCN, Frame) 1$ {S\; C\;{N_{winner}({Frame})}}arrow{\underset{i = 0}{\min\limits^{N}}\{ {S\; C\;{N\lbrack i\rbrack}} \}} $2 for i ← 1 to N 3  if SCN[i] == SCN_(winner) 4  return WRAN_(winner)(Frame) ← WRAN[i] and SCN_(winner)(Frame)Where in the algorithm,

N: total number of contending WRAN cells;

WRAN: the array of IDs of the contending WRAN cells, WRAN[i] for i←1 toN;

SCN: the array of spectrum contention numbers of the contending WRANcells, in which SCN[i] is the spectrum contention number of WRAN[i] fori←1 to N;

Frame: the data frame (spectrum resource) being contended for; (targetframe)

SCN_(winner)(Frame): the winner spectrum contention number for accessingthe Frame; and

WRAN_(winner)(Frame): the ID of the winner WRAN cell to access theFrame.

Each contending WRAN cell produces and sends to the destination cell aspectrum contention number. According to one embodiment of the presentinvention the spectrum contention number, SCN_(i), for WRAN cell i,WRAN_(i), is generated, according to one embodiment of the presentinvention, as:SCN_(i)=RANDOM(0,2^(X)−1).

As presented above, the winning WRAN cell of a frame-based, on-demandinter-WRAN spectrum contention is the WRAN cell possessing the smallestspectrum contention number. One reasonably skilled in the relevant artwill recognize that other techniques can be used to generate a spectrumcontention number. Indeed, the algorithm presented above for resolutionof a spectrum contention may vary without departing from the scopecontemplated by the present invention.

As shown above, a spectrum contention destination collects, over apredetermined period of time, one or more spectrum contention numberswherein each spectrum contention number is generated and issued to thedestination cell by a WRAN source cell contending for use of the sharedspectrum. The destination cell builds from the received spectrumcontention numbers an array comprised of each received SCN. Each SCN inthe SCN array is associated with its generating WRAN identificationnumber. A similar array of contending WRAN cells is fabricated andcomprised of the WRAN identification numbers.

According to one embodiment of the present invention, the determinationof a minimum SCN necessarily identifies a WRAN cell associated with thatminimum SCN. Thus, for a particular shared resource frame, a winningWRAN cell, WRAN_(winner), is determined. Thereafter, the winning WRANcell ID along with the winning SCN is broadcast from the WRAN cellconducting the contention.

FIG. 5 shows a flowchart of a frame-based, on-demand spectrum contentionprotocol according to one embodiment of the present invention. Uponinitiation 505 of a contention, (block 350 of FIG. 3) the destination ordeciding WRAN cell determines whether the contention is based on aninternal or external demand for additional access to the shared spectrumresource.

Recall that an external demand 510 for acquiring access to the occupiedframes may be the result of a new or existing base station seeking moredata service bandwidth. Upon determining that an external inter-WRANdemand for acquiring access to the occupied frames 510 exists, thedestination WRAN cell initiates a contention 520 for the targeted dataframes while still behaving as a spectrum contention destination(explained in detail with reference to FIG. 9). As the spectrumcontention destination, the WRAN cell is in control of the evaluationprocess of the spectrum contention numbers, although the process itselfis equitable and gives the destination cell no inherent advantages.

When a determination is made that an internal intra-WRAN demand 530 foradditional frames occurs, the destination WRAN cells first identify 540available (non-occupied) frames in the superframe structure. This isdone with reference to a superframe MAP. The superframe MAP identifiesframe allocation within a superframe of a particular channel for aspecific one hop WRAN neighborhood. Recall that an internal demandoccurs when a destination or controlling WRAN cell experiences anincreased need for data bandwidth due to internal alterations such asmore usage by or presence of CPEs within its area of coverage. Since theincreased demand is internal, it is likely that the current state ofshared spectrum allocation is not challenged by the other participatingWRAN cells. Thus, it may be possible to reallocate resources withouthaving to enter a full contention procedure as a contention may resultin a decrease of the destination's current resource allocation.

Once available data frames are identified 540, a course of action isundertaken to acquire 550 one or more of the non-occupied data frames soas to meet the increased internal demand (explained in detail withreference to FIG. 6). Upon acquisition of the new data frames, a queryis made 560 whether additional data frames are needed to meet theinternal intra-WRAN spectrum demand.

If no additional frames are needed, the process ends 595 (returning toblock 360 of FIG. 3). Note that when a destination WRAN cell experiencesan internal demand and the superframe structure includes non-occupied ornon-used data frames, a contention for shared spectrum resources is notnecessary.

When the acquisition of non-occupied frames fails 560 to meet theincreased internal need, the destination WRAN cell selects 570 targetdata frames from the occupied data frames in the superframe MAP. Onceselected, the WRAN cell seeking additional data frames based on aninternal intra-WRAN spectrum demand initiates a contention 580(explained in detail with reference to FIG. 8). The contention 580 isfor the targeted frames and does not involve the frames which itcurrently occupies. Thus, the cell seeking a contention to resolve itsinternal intra-WRAN spectrum demand assumes the role of a spectrumcontention source, SC-SRC. To the other WRAN cells using the sharedspectrum resources, an external demand 510 for their data frames hasjust occurred.

Upon receiving the spectrum contention request the cell(s) occupying thetargeted frames conduct a contention as previously described. As will beunderstood by one of reasonable skill in the relevant art, the result ofthe contention is unpredictable. It is possible that the cellexperiencing the internal intra-WRAN spectrum demand may win thecontention, gaining access to new data frames thus resolving itsinternal demand. However, the losing WRAN cell may then experience aninternal demand for additional data frames. The losing cell now entersthe flowchart shown in FIG. 5 to resolve its demand by determiningwhether the demand is internal 530 or external 510. The contention mayalso result in the WRAN cell seeking the additional cells losing thecontention. In such a case, no additional resources have been gainedfrom the contention which will likely spark the need for an additionalcontention.

In conjunction with the acquisition of the additional data frames fromeither an externally or internally generated demand, a WRAN cell needsto determine the availability of data frames within the superframestructure in which it is operating. FIG. 6 represents a high levelflowchart of one method embodiment of the present invention fordetermining the availability of data frames in an on-demand sharedspectrum environment.

Determining frame availability begins 605 with marking 610 all of theknown available (non-occupied) frames within a superframe structure aswinner frames. With the frames identified as winner frames, a WRAN cellseeking additional data frames can initiate acquisition of the winningdesignated frames should no other claim of ownership exist. Thus, theprocedure's next task is to determine whether another WRAN cell hasgained access and control of a particular data frame. Recall that eachWRAN cell possesses a sensing or listening (quiet) period in which itgathers information broadcasted from other base stations. It is duringthis period of the beacon window 260 in which a WRAN cell looking togain additional frames would find out if another nearby WRAN cell hasgained ownership of a particular data frame. Upon time out 615 of thatsensing period, a WRAN cell which has designated a frame as a winningframe can initiate acquisition procedures. Said another way, since noother WRAN cell has indicated that is has a controlling interest in aparticular frame, it is free to acquire the data frame for its own use.

However, it is possible that during this sensing period the WRAN cellmay receive 630 a spectrum contention release message, SC-REL. Such amessage would indicate that a particular frame, F_(x), has been releasedto WRAN N where N is the WRAN identification number. Just as previouslydiscussed in reference to FIGS. 1 and 3, it is possible that the WRAN Nand the WRAN cells seeking additional data frames are not within one-hopof each other. Thus, upon receiving such a SC-REL message, the WRAN celldetermines 640 whether WRAN N is a one-hop neighbor. When WRAN N is nota one-hop neighbor, then the release of a particular frame to WRAN Ndoes not preclude the WRAN cells seeking additional data frames fromseeking their acquisition. In such a case a query is made to determinewhether F_(x) is on the list of available frames. If it is, the list ofavailable frames is updated 670 (in this case confirming no change) andall available frames are again marked as being winning frames 610.

When the query determines that F_(x) is not on the list of availableframes, F_(x) is added 665 to the list and the list is updated 670. Thisiterative inquiry operates until a robust list of available frames isdetermined, all of which are marked as winner frames 610.

When the inquiry of whether WRAN N is a one hop neighbor 640 isaffirmative, an additional inquiry is made with respect to the status ofF_(X) and its existence on the list of available frames 645. If F_(X) isnot on the list of available frames no change is necessary as F_(X) isnot available. However, if F_(X) is on the list of available frames itis accordingly removed 650. Since WRAN N is a one hop neighbor and a RELmessage has been issued indicating F_(X) has been released to WRAN N, itcannot also be occupied by another one hop WRAN cell.

With the list of available frames constructed and each available framemarked as a winner frame 610, the inquiry once again turns to see if asource contention frame release message is received. When no suchmessage is received during a sensing period 615, a spectrum contentionnumber N_(C) is generated 620 and the frame acquisition procedure 625(explained in detail with reference to FIG. 7) is initiated 695(returning the process to block 560).

FIG. 7 is a flowchart of one embodiment of the present invention forframe acquisition in a frame-based, on-demand spectrum contentionenvironment. The flowchart depicted in FIG. 7 begins 705 upon initiationof the frame acquisition procedure introduced in FIG. 6 625 and FIG. 8890. With a list of available frames in hand, the WRAN cell seekingadditional data frames, WRAN_(C), broadcasts 710 a message, SC-ACK,containing a spectrum contention number N_(c) announcing its intent toacquire the winner frames beginning upon commencement of the nextsuperframe.

In response to broadcasting such an acknowledgement message one of threescenarios can occur. First, no other messages are received during thesensing period meaning that no contention for the winning frames willoccur. Second, the broadcasting WRAN cell, WRAN_(C), can receive arelease message having another spectrum contention number indicatingthat another WRAN cell, WRAN_(K), has been granted access to, andcontrol of, the same frame. And third, another acknowledgement messagecan be received from another WRAN cell, WRAN_(M), announcing that it toois attempting to acquire the same data frame. Each of these scenarios isdescribed below in detail.

If, during the sensing period, the broadcasting WRAN_(C) cell receivesanother spectrum contention acknowledgement message, SC-ACK 720 fromWRAN_(X), the cells must determine which cell has priority to the dataframe. Recall that for another WRAN cell to issue an acknowledgementmessage in an attempt to acquire a data frame it has similarlydetermined a list of available frames. Thus, this type of acknowledgmentmessage is from a one-hop neighbor. Just as original SC-ACK messageincludes a spectrum contention number N_(C), so too does theacknowledgement message from WRAN_(M), N_(X). To determine which WRANcell will acquire the available data frame, a comparison 750 of thespectrum contention numbers takes place. If N_(C) is smaller than N_(X),WRAN_(C) wins the contention and thereafter issues a broadcast messagein the next beacon window 260 acknowledging its intent to acquire awinning frame at the beginning of the next superframe.

The losing WRAN, in this case WRAN_(M), removes its intent to acquirethe frame and is silent during the next beacon window 260. Likewise, ifWRAN_(C) lost the contention, it would no longer pursue that frame(marking it as a loser frame 755) and upon arrival of the next beaconwindow 260, it would remain silent and likely receive an acknowledgementmessage from WRAN_(M) of its success in acquiring that frame.

One possible outcome of WRAN_(C)'s broadcast of its intention to acquirethe winning frame(s) from the available frame listing is the receipt ofa spectrum contention release message 730, SC-REL, from a spectrumcontention destination, SC-DST. Recall that after a contention, adestination WRAN issues a release message indicating which WRAN cell isgaining control of a particular sheared spectrum resource. In this case,WRAN_(C) after issuing its broadcast acknowledgement message of intentto acquire one or more available frames in a particular superframestructure, may receive a spectrum contention release, SC-REL, indicatingthat WRAN_(K) has been granted the right to acquire the same frame as isbeing sought after by WRAN_(C). Included in the SC-REL message is thespectrum contention number, N_(X), generated by WRAN_(K). (note:WRAN_(M) and WRAN_(K) can be the same WRAN)

Recall that the destination cell releasing a shared spectrum resource, aframe, is a one-hop neighbor of WRAN_(C). However, the cell to which thespectrum contention destination is releasing the frame may or may not bea one-hop neighbor of WRAN_(C). And, if the cell gaining control of thesought after frame is not a one-hop neighbor, the frame from WRAN_(C)'sperspective, is still available for use.

Accordingly, the next step in one embodiment of the procedure for frameacquisition, as shown in FIG. 7, is to determine if WRAN_(K) is aone-hop neighbor of WRAN_(C) 740. When it is determined that WRAN_(C)and WRAN_(K) are not one-hop neighbors, another message is broadcast,this time without likely receipt of a SC-REL message indicating thatanother WRAN has been granted control of the same frame.

When the inquiry 740 determines that WRAN_(C) and WRAN_(K) are one-hopneighbors, a comparison of each cell's spectrum contention number iswarranted. N_(C) and N_(X) are compared 750, in one embodiment of thepresent invention, with the smaller spectrum contention number winning.When the result is such that N_(C) is smaller than N_(X), the processrecognizes a victory and another acknowledgement message is broadcast.And, when it turns out that N_(X) is smaller than N_(C), WRAN_(C)accepts the failure and can consider whether the initiation of anothercontention at a later time is warranted. One of reasonable skill in theart will understand that N_(X) of WRAN_(M) is distinct from N_(X) ofWRAN_(K).

FIG. 7 shows that the last option, post issuing a broadcastacknowledgment message announcing intent to acquire a particular sharedspectrum resource, is silence. It is possible that after the SC-ACKmessage is issued, no other acknowledgments, SC-ACK, or other releases,SC-REL, are received. Upon expiration of a predetermined time out period760 the WRAN seeking control of a particular winning frame, in thisexample WRAN_(C), can mark the winning frame(s) as occupied 770. Oncemarked, the frames are occupied in the upcoming superframe for datatransport and remain occupied until a new contention is received 795.The superframe MAP is modified and announced accordingly.

According to one or more embodiments of the present invention, aspectrum resource contention is a dispute over the control of a sharedspectrum resource. While a spectrum resource can be expansively defined,it can, in one embodiment of the present invention, comprise one or moredata frames. The resolution of a dispute as to which WRAN cell willcontrol and occupy a particular data frame or similar shared spectrumresource is fundamental to a frame-based, on-demand spectrum contentionprotocol.

An exemplary depiction of a shared spectrum contention from the spectrumcontention source's perspective is depicted in the flowchart of FIG. 8.According to one embodiment of the present invention, a contentionbegins 805 with identifying 810 the occupiers of targeted frames.(reference block 580 of FIG. 5) By definition the WRAN cell thatoccupies a frame (shared spectrum resource) is a spectrum contentiondestination. The “destination” designation is derived from its role asthe destination of one or more contention requests for access to theframe which is under its control.

Once a WRAN cell, WRAN_(C), has identified which of its neighbors is/areoccupying a sought after data frame(s) a spectrum contention number,N_(C), is generated 820. A separate spectrum contention number isgenerated for each destination in which a contention is contemplated. Inother embodiments of the present invention, a spectrum contention numberNC could be generated for each frame under contention. By generating aspectrum contention number for each destination, the conveyance ofinformation necessary to conduct the contention is minimized.

With a spectrum contention number in hand, the WRAN cell, acting as asource of a contention, SC-SRC, issues a spectrum contention request830, SC-REQ, message to each of the targeted destination(s) withtargeted frames occupied by that destination marked in the vector.Included in the SC-REQ is the newly generated spectrum contentionnumber, N_(C). As previously discussed, the resolution of a spectrumcontention occurs at the destination WRAN. Consequently, once the SC-REQhas been issued, the issuing WRAN, in this example WRAN_(C), waits untila response message, SC-RSP, is received 840 from each of thedestinations to which a SC-REQ has been directed (reference FIG. 9).Note that while this and other examples herein are described in singularcontext, a request for additional data frames and a subsequentcontention procedure can occur for multiple frames within the samesuperframe and among multiple channels, simultaneously. Indeed a WRANmay easily occupy multiple roles of being both a spectrum contentiondestination and source with respect to different frames on the same ordifferent channels at the same time.

A spectrum contention continues upon receipt of a response message froma destination WRAN cell 850. The SC-RSP will provide the source of thecontention request with the results of the contention. If the requestingWRAN cell, the SC-SRC, possesses a winning spectrum contention number,then the response will indicate that it has won the contention.Alternatively, if the requesting WRAN cell's spectrum contention numberwas insufficient to secure a victory, the response message will indicatethat another WRAN cell, possibly the destination WRAN cell, is thevictor.

Upon receipt of the response message the frames in which victory wassecured are marked 860 as winner frames. Thus, consider a situation inwhich a requesting WRAN is seeking access to three data frames allcontrolled by another one-hop neighbor WRAN cell. The three frames,having been identified as being occupied, are the focus of a spectrumcontention request which includes, in one embodiment of the presentinvention, a unique spectrum contention number for each frame. Uponreceiving the request, the destination conducts a comparison of thereceived spectrum contention numbers and its internally generatedspectrum contention numbers (assuming that the destination cell desiresto remain in control of the frames under contention) as well as anyother contention numbers for other participating cells. It is possiblethat of the three data frames sought by the source WRAN cell, only oneor two of the contentions will be successful. In these successful cases,the targeted frames are marked 860 as being winner frames. The deniedframe(s) are accordingly marked as loser frames 870.

Once the frames are marked, another sensing period is undertaken todetermine whether additional response messages have been issued 840. Atthe end of a predetermined period of time, a time out period for frameacquisition 880, the WRAN cell moves to acquire 890 control and accessto the winner data frames (explained in detail with reference to FIG.7). Upon acquisition, and thus use for data transfer, the contentionprocess ends 895 (returning the process to 595 of FIG. 5 and thus 360 ofFIG. 3).

FIG. 9 is a flowchart of a procedure for a destination basedframe-based, on-demand spectrum contention according to one embodimentof the present invention (reference block 520 of FIG. 5). Resolution ofa contention takes place at the WRAN cell which currently controls andoccupies the targeted shared spectrum resources. As discussed, such acell is designated as the destination of the contention.

From a spectrum contention destination cell's perspective, a contentionbegins 905 with either the receipt of a spectrum contention request 910or a spectrum contention acknowledgement 960.

Upon receiving 910 one or more spectrum contention request messagesduring a spectrum contention window from one or more spectrum contentionsource WRAN cells, the messages are decoded 915 to identify individualWRAN cells and their respective spectrum contention numbers. Having inits possession the spectrum contention numbers from other sourcespectrum contention cells, the spectrum contention destination generatesits own spectrum contention number, N_(C) 920.

As previously discussed a contention may involve more than one framewithin the superframe structure. According to one embodiment of thepresent invention, the spectrum contention destination process selects925 an occupied frame, F_(C), that is being contended for by one or moresource cells. (Note that the multiple frames F_(C) can be occupied bythe same destination WRAN) As previously described, each spectrumcontention request includes its own spectrum contention numberassociated with each WRAN cell. In one embodiment of the presentinvention a WRAN cell SRC seeking two targeted frames, F₁ and F₂, wouldonly issue on NC. In another embodiment of the present invention, aspectrum contention number can be associated with each frame F_(C). Thecomparison 930 is thereafter conducted for the targeted frames, F_(C),between the spectrum contention number, N_(C), of the spectrumcontention destination and the spectrum contention numbers, N_(X), ofthe source cells.

When the spectrum contention number, N_(C), is smaller than all spectrumcontention numbers, N_(X), carried in all the spectrum contentionrequest messages for the contended frame, F_(C), a contention success(the destination's perspective) for those particular data frames isdeclared 945. When a success is declared for the destination, a SC_RSPmessage is constructed using a frame vector issued to each SC_SRCindicating that F_(C) is not granted. And, alternatively, when thespectrum contention number, N_(C), is larger than all spectrumcontention numbers, N_(X), carried in the spectrum contention requestmessages for the contended frame, F_(C), a failure is declared 935(reference block 1005 of FIG. 10). Frames in which a spectrum contentionfailure has been declared are marked as “to-be-released” once anacknowledgment has been received from the winning WRAN (see below).

A comparison of the spectrum contention numbers, N_(X), received fromeach spectrum contention request, SC-REQ, and the spectrum contentionnumber, N_(C), generated by the spectrum contention destination, isconducted for each occupied frame that is in contention 940. Upon theresolution of contention for each occupied frame identified by thereceived spectrum contention request messages, a release is pending 950(reference block 1105 of FIG. 11). For the frames in which a contentionfailure has been identified the release message would indicate that thewinning spectrum contention source has gained control of the designatedframe. And, in the situation wherein the spectrum contention destinationwas victorious in the contention, the release message would indicatethat control of the applicable frame would remain with the spectrumcontention destination. With the release pending 950 a release messageis generated 955 containing the winning spectrum contention numberannouncing to the winning WRAN cell that F_(C) is released at the startof the next superframe.

The other possible initiation of a shared spectrum contention is uponreceipt 960 of a spectrum contention acknowledgment message, SC-ACK,containing a spectrum contention number, N_(X), from a neighboringWRAN_(M) cell announcing its intent to acquire a frame which iscurrently occupied by the destination. For example, with additionalreference to FIG. 2, a contention process between Network 1 210 andNetwork 2 220 can result in Network 2 220 issuing an acknowledgementmessage to Network 3 230. It is this additional acknowledgement messagebetween Network 2 220 and Network 3 230 from the contention betweenNetwork 1 210 and Network 2 220 that is the subject of SC_ACK message ofFIG. 9 960. Upon receipt of such an acknowledgment message, the frameunder contention, F_(X), is marked as a frame to be released 965. Recallthat a spectrum contention acknowledgment message is generated upon thedetermination that a frame is available. Thus, upon receipt of aspectrum contention acknowledgment message, no contention is required.

Accordingly, once the frame, F_(X), has been marked to be released 965,a spectrum contention release message is broadcast to announce that theframe, F_(X), will be released 970 to WRAN_(M) starting from the nextsuperframe.

Upon expiration of a predetermined period of time, all frames marked as“to-be-released” starting from the next superframe are released 980 atthe beginning of the next superframe. The process thereafter ends 995(reference block 595 of FIG. 5). A corresponding spectrum contentionresponse message is constructed by the destination using frame vectorsfor all spectrum contention sources in which the contention was notsuccessful and access to the targeted frame was not gained.

FIG. 10 is a high level flowchart of a spectrum contention failure for adata frame at a spectrum contention destination involving multipleframes, according to one embodiment of the present invention (referenceblock 935 of FIG. 9). Recall that a spectrum contention destination maybe in control of more than one frame of a 16 frame superframe structure.Upon receipt of a spectrum contention request, the above-describedcontention process is undertaken to determine whether occupancy of theframe will remain with the destination or whether the frame will bereleased.

Upon determination that, from the destination's perspective, thecontention for a frame has failed, a process is begun 1005 to identify1010 the winning spectrum contention source for each frame. Recall thatin the previous method the destination simply determined that incomparison with the received spectrum contention numbers, its owninternally generated spectrum contention number was insufficient tomaintain control and occupancy of the targeted spectrum resource.Thereafter, and according to one embodiment of the present invention, adetermination is made to identify 1010 which spectrum contention sourcefor a particular frame, F_(C), is associated with the winning spectrumcontention number.

Once the winning spectrum contention source has been identified for eachframe F_(C), a spectrum contention response message is constructed 1030using frame vectors to the winning spectrum contention source informingit of its victory. Likewise, for all remaining spectrum contentionsources in which the attempt to gain access to frame F_(C) was afailure, a spectrum contention response message is constructed 1040 bythe destination (again using frame vectors) informing the spectrumcontention sources that the attempt to gain access to frame F_(C) hasfailed.

FIG. 11 is a high level flowchart of the release of pending operationsat a contention destination, according to one embodiment of the presentinvention. Upon construction of the success and failure spectrumcontention response messages, the messages are sent 1150 to theappropriate source WRAN cells by the destination. After the spectrumcontention response, SC-RSP, message is sent, the destination waits 1160a predetermined period of time for a spectrum contention acknowledgmentfrom each source. When an acknowledgment message, SC-ACK, is received1170 from the winning spectrum contention source WRAN the frame, F_(C),is marked as “to-be-released” 1180. The process iteratively continues,waiting for additional SC_ACK messages 1160, until a time out period isobtained 1190 ending the process 1195.

As shown above, a WRAN cell, acting as a spectrum contention destinationor a spectrum contention source, can effectively and efficiently manage,gain and release shared spectrum resources on a frame-by-frame basisover the superframe structure. Thus, according to one embodiment of thepresent invention, data frames of any superframe of a spectrum resourcecan be reallocated on a frame-by-frame basis beginning with eachsuperframe as the needs of the WRAN cells within a cognitive radiocommunication network vary.

One of reasonable skill in the relevant art will appreciate that areliable and efficient inter-network communication mechanism forcoexistence is necessary for WRAN cells to effectively execute aframe-based, on-demand spectrum contention protocol. One means by whichto establish inter-network communication is via the beacon windowfollowing each data frame. Other communication mechanisms are possibleand may be modified to align with the teachings and spirit of thepresent invention. With the synchronization of the frame/superframestructure between inter-network WRAN cells a fine grain spectrum sharingis achievable.

As discussed above, inter-network communication can occur, according toone embodiment of the present invention, via spectrum contentionmessaging such as request, response, acknowledgement and releasemessages. The messages are transmitted in the payload of a contentionbeacon period packet.

According to one embodiment of the present invention, a spectrumcontention request message, SC-REQ, can be of the following format.

Syntax Size Notes SC_REQ_IE_Format( ) {  Element ID  8 bits Indicationof the Message Type  Length  8 bits  BS ID of 48 bits The MAC address ofthe contention source's base  Contention Source station.  BS ID of 48bits The MAC address of the contention destination's base  Contentionstation.  Destination  Sequence number  8 bits Incremented by 1 by thesource whenever any of the following three fields change. The contentiondestinations shall discard the repeated SC_REQ IEs.  Spectrum 16 bits Arandom number to show the priority to contend for  Contention spectrumresource of the target TV channel.  Number (SCN)  TV Channel  8 bits TheTV channel being requested by the contention  number source  Contention16 bits A bit vector indicating the indexes of data frames  RequestFrame within a superframe that the Contention Source  Index Vector WRANrequests to acquire (through the contention) for its data servicesstarting from the next superframe. For each of the 16 bits as shownbelow, the corresponding frame is requested for the contention when abit's value is set to 1. Otherwise, the bit value of the correspondingframe is set to 0. Bit 0: Frame 0; Bit 1: Frame 1; Bit 2: Frame 2; Bit3: Frame 3; Bit 4: Frame 4; Bit 5: Frame 5; Bit 6: Frame 6; Bit 7: Frame7; Bit 8: Frame 8; Bit 9: Frame 9; Bit 10: Frame 10; Bit 11: Frame 11;Bit 12: Frame 12; Bit 13: Frame 13; Bit 14: Frame 14; Bit 15: Frame 15.}

A spectrum contention response message, SC-RSP, is sent to inform acontention source whether a request for a targeted spectrum resource(frame) was successful. As discussed herein, such a message istransmitted from a destination WRAN after it has received a spectrumcontention request message. A spectrum contention response message canbe, according to one embodiment of the present invention, of thefollowing format.

Syntax Size Notes SC_RSP_IE_Format( ) {  Element ID 8 bits Indication ofthe Message Type  Length 8 bits  BS ID of the 48 bits  Copy from thecorresponding CC_REQ IE received  Contention Source  BS ID of the 48bits  MAC address of the Spectrum Contention Destination BS.  Contention Destination  Sequence number 8 bits Copy from the CC_REQ.  TV Channel 8bits The TV channel requested by the Contention Source BS  number Contention 16 bits  A bit vector indicating the contention resultsdetermined by the  Response Frame channel contention algorithm for thedata frames within a  Index Vector superframe that the contention sourceWRAN requests to acquire. These contention results will be effectivestarting from the next superframe. For each of the 16 bits as shownbelow, the corresponding frame is granted to the contention source whena bit's value is set to 1. Otherwise, the frame is not granted. For adata frame that is not requested by any contention source, thecorresponding bit is set to 0. Bit 0: Frame 0; Bit 1: Frame 1; Bit 2:Frame 2; Bit 3: Frame 3; Bit 4: Frame 4; Bit 5: Frame 5; Bit 6: Frame 6;Bit 7: Frame 7; Bit 8: Frame 8; Bit 9: Frame 9; Bit 10: Frame 10; Bit11: Frame 11; Bit 12: Frame 12; Bit 13: Frame 13; Bit 14: Frame 14; Bit15: Frame 15. }

The spectrum contention acknowledgement message of the present inventionis typically sent in a contention beacon period burst payload by thecontention source. It is used to notify contention destinations that thecontention source will occupy the destination's working shared spectrumor give up a request to do so. For example, a contention source willtypically notify a contention destination that it will occupy a sharedspectrum resource when it receives a response message with a contentionsuccess indication from all of the contention destinations. Otherwise,the contention source will notify the contention destinations that itwill relinquish control of the shared spectrum resource if it receives aresponse message with a rejection indication from any of the contentiondestinations. According to one embodiment, the format of anacknowledgment message is the following.

Syntax Size Notes SC_ACK_IE_Format( ) {  Element ID  8 bits  Length  8bits  Source Id 48 bits The MAC address of the contention source Destination (Broadcast) 48 bits The MAC address of Message Broadcast Id  Sequence number  8 bits Same as the corresponding SC_REQ IE. Thecontention destinations shall discard the repeated CC_ACK IE beingreceived  TV Channel number  8 bits The TV channel being requested bythe contention source  Contention 16 bits A bit vector indicating thecontention results determined by  Acknowledgement the channel contentionalgorithm for the data frames within  Frame Index Vector a superframethat the contention source WRAN will acquire starting from the nextsuperframe. For each of the 16 bits as shown below, the correspondingframe will be occupied by the contention source when a bit's value isset to 1. Otherwise, the frame will not be occupied. Bit 0: Frame 0; Bit1: Frame 1; Bit 2: Frame 2; Bit 3: Frame 3; Bit 4: Frame 4; Bit 5: Frame5; Bit 6: Frame 6; Bit 7: Frame 7; Bit 8: Frame 8; Bit 9: Frame 9; Bit10: Frame 10; Bit 11 Frame 11; Bit 12: Frame 12; Bit 13: Frame 13; Bit14: Frame 14; Bit 15: Frame 15. Spectrum Contention 16 bits The winningSCN used in SC_REQ message, showing the Number (SCN) priority to contendfor spectrum resource of the target TV channel. BS ID of the grantingSC- 48 bits The ID of the SC-DST WRAN cell granting the access to DSTthe data frame that are being acquired by the winning SC- SRC (this isused to enable “clear to send”). }

And, similarly, a spectrum contention release message is typically abroadcast type of message transmitted by the spectrum contentiondestination which has granted access to a particular shared spectrumresource announcing the resource's release. A typical release message,according to one embodiment of the present invention, can be of thefollowing format.

Syntax Size Notes SC_REL_IE_Format( ) {  Element ID  8 bits  Length  8bits  Source Id 48 bits The MAC address of the contention destinationBS.  Destination (Broadcast) 48 bits The MAC address of MessageBroadcast  Id  Sequence number  8 bits Same as the corresponding CC_REQIE. The contention destinations shall discard the repeated SC_REL IEbeing received  TV Channel number  8 bits The TV channel being requestedby the contention source  Contention Release 16 bits A bit vectorindicating the contention results determined by  Frame Index Vector thechannel contention algorithm for the data frames within a superframethat the contention source WRAN will acquire starting from the nextsuperframe. For each of the 16 bits as shown below, the correspondingframe will be occupied by the contention source when a bit's value isset to 1. Otherwise, the frame will not be occupied. Bit 0: Frame 0; Bit1: Frame 1; Bit 2: Frame 2; Bit 3: Frame 3; Bit 4: Frame 4; Bit 5: Frame5; Bit 6: Frame 6; Bit 7: Frame 7; Bit 8: Frame 8; Bit 9: Frame 9; Bit10: Frame 10; Bit 11 Frame 11; Bit 12: Frame 12; Bit 13: Frame 13; Bit14: Frame 14; Bit 15: Frame 15. Spectrum Contention 16 bits The winningSCN used in SC-REQ message, showing the Number (SCN) priority to contendfor spectrum resource of the target TV channel. BS ID of the winning SC-48 bits The ID of the the SC-SRC WRAN cell granted the access to SRC thedata frame that are being released by the granting SC- DST (this is usedto enable efficient spectrum reuse). }

The frame-based, on-demand spectrum contention protocol of the presentinvention provides an efficient, scalable, and fair internetworkspectrum sharing system. The protocols of the present invention providesimple contention processes using a random number exchange. Contentionsare conducted in parallel with ongoing data transmissions. Thus, thereis no interruption in data communications. Collisions are avoided andthere are no hidden node problems. The protocols of the presentinvention are scalable in that the decision-making process isdistributed with no central arbitrators needed. The process is stableproviding cooperation among the networks achieving a needed goal offairness and efficiency in spectrum sharing.

The frame-based, on-demand spectrum contention protocol presented hereinis also fair. By using a random number comparison and an on-demanditerative contention process, the allocation of shared network resourcesare equitably distributed. To verify the equity of the protocols of thepresent invention multiple coexistence scenarios were conducted usingperformance evaluation and tools.

Using the NS2 model network simulator under IEEE 802.22, a performanceevaluation of the protocols of the present invention were conducted. Thesimulation parameters included sharing a single channel in which eachsuperframe is comprised of 16 frames. Each frame within the superframeis 10 ms in length and the self-coexistence window is 1 ms. Thesimulations were conducted over a 10,000 second period of time.

Three coexistence scenarios were examined including a complete graphscenario, a cycle graph scenario and a wheel graph scenario. FIG. 12shows a graphical representation of various coexistence scenarios usedin the simulation evaluation. Each graphical depiction identifies aplurality of the stations or WRAN cells and their respectivecommunication paths.

The first coexistence scenario examined under the simulation conditionsdescribed above was a complete graph scenario comprised of four basestations. As shown in FIG. 12 a 1210 each of the four base stations cancommunicate with the other three base stations in the complete graphscenario. Thus, the scenario represents a situation where the WRAN cellsof each station overlap. The result of the simulation, shown in thetable below, identify the fairness of the frame-based, on-demandspectrum contention protocol of the present invention. For example,theoretically, a perfectly fair sharing of a spectrum resource betweentwo cells would result in a 0.5 usage of the spectrum for each cell. Asshown in the table below, the present invention identifies that in a twocell scenario the first cell gained access to the shared spectrum0.500884 times as compared to sell two which had access to the sharedspectrum of 0.494989. And as shown in the last column, it took 30seconds to achieve convergence of this equality.

The remaining entries in the table indicates scenarios of 3, 4, and 5cell networks. Again, for example, and in correspondence with thedepiction of a complete graph scenario shown in FIG. 12 a 1210, a fourcell complete graph scenario experienced convergence within 270 seconds.Each of the four cells achieved approximately ¼ of the total access tothe shared spectrum. The entries under cell 1, cell 2, cell 3 and cell 4represent the actual access to the shared spectrum for each of therepresentative cells. Thus, after 270 seconds, with respect to the totalaccess to the shared spectrum, cell 1 achieved a 0.248409 portion, cell2 achieved a 0.251128 portion, cell 3 achieved a 0.251106 portion andcell 4 achieved a 0.246233 portion.

TABLE 1 Complete Graph Scenario No. of Convergence Cells Cell 1 Cell 2Cell 3 Cell 4 Cell 5 Optimal Time(s) 2 0.500884 0.494989 ½ 30 3 0.3316300.329914 0.335365 ⅓ 150 4 0.248409 0.251128 0.251106 0.246233 ¼ 270 50.202269 0.193133 0.203893 0.198870 0.198137 ⅕ 300

The second performance evaluation of the present invention involved acycle graph scenario. As shown in FIG. 12 b, a cycle graph scenario isone in which a plurality of the WRAN cells overlap with thecommunication paths being limited. The depiction shown in FIG. 12 b isof 5 overlapping WRAN cells in which any one WRAN cell overlaps withonly two one-hop neighbors.

The evaluation of the cycle graph scenario shown in FIG. 12 b 1220demonstrates the convergence occurs more quickly for combinations ofWRAN cells that can be grouped. For example, the convergence of threeWRAN cells occurs in 150 seconds while the convergence of 6 WRAN cellsoccurs in 30 seconds. Correspondingly, the convergence of five WRANcells occurs in 336 seconds. The reason for this is because six WRANcells can be grouped into three sets of two WRAN cells and similarlyfour WRAN cells can be grouped into two sets of two WRAN cells. However,numbers such as five and seven WRAN cells cannot be grouped efficientlythus resulting in a higher convergence time. (See below)

TABLE 2 Cycle Graph Scenario No. of Convergence Cells Cell 1 Cell 2 Cell3 Cell 4 Cell 5 Cell 6 Cell 7 Optimal Time(s) 3 0.331630 0.3299140.335365 ⅓ 150 4 0.501248 0.495934 0.495934 0.500581 ½ 32 5 0.4200310.284119 0.419478 0.416048 0.4197 ⅖ 336 6 0.497953 0.498706 0.4978220.498873 0.497619 0.4989 ½ 30 7 0.430724 0.448526 0.428689 0.4368940.439151 0.432226 0.348478 3/7 418

As with the simulation scenario involving a complete graph, a cyclegraph scenario also provides equitable results. For example, in thecycle graph of 3 WRAN cells each achieves access to approximately ⅓ ofthe shared spectrum. As shown above, cell 1 achieves a 0.331630 portionaccess, cell 2 achieves a 0.329914 portion access and cell 3 achieves a0.335365 portion access to shared spectrum. In a four cell example,access is based on a two cell grouping. Thus, for an equitabledistribution of the shared spectrum any one cell should achieveapproximately a 0.5 portion access to the shared spectrum. As can beseen in the results shown in the table above, each cell in a four cellscenario achieves approximately a 0.5 portion access to the sharedspectrum and does so with a convergence of approximately 32 seconds.Similar equitable results can be seen for scenarios of 5, 6 and 7 WRANcell networks.

The final scenario for the performance evaluation of a frame-based,on-demand spectrum contention protocol is that of a wheel graph scenario1230. A wheel graph scenario is one of the plurality of WRAN cells inwhich each cell overlaps with and can communicate with each other cell.Again, as with the cycle graph scenario, convergence is optimized whencells can be grouped. For example a five WRAN cell scenario can beoptimized by examining the convergence of groups of three WRAN cells.

TABLE 3 Wheel Graph Scenario No. of Convergence Cells Cell 1 Cell 2 Cell3 Cell 4 Cell 5 Cell 6 Cell 7 Optimal Time(s) 4 0.248409 0.2511280.251106 0.246233 ¼ 270 5 0.334881 0.333089 0.32877 0.334587 0.327745 ⅓505 6 0.283983 0.277948 0.305698 0.278366 0.283266 0.278926 2/7 1933 70.324517 0.335407 0.336619 0.330762 0.330051 0.329977 0.331971 ⅓ 1112

Table 3 above shows that an optimal conversion of four WRAN cells in awheel graph scenario is approximately ¼ of the shared spectrum. Thus,each of the 4 WRAN cells should gain approximately a 0.25 portion accessto the shared spectrum upon convergence. The result of the simulationabove shows that after 270 seconds, cell 1 achieved a 0.248409 portionaccess, cell 2 achieved a 0.251128 portion access, cell 3 achieved a0.251106 portion access and cell 4 achieved a 0.246233 portion access toshared spectrum. Similarly, in a five WRAN cell wheel graph scenario,the optimal convergence occurs by a grouping of three cells. Thus, eachof the three grouped cells should achieve approximately a ⅓ portionaccess to the shared spectrum upon convergence. The result of thesimulation shows that in a five cell wheel graph scenario, cell 1achieved a 0.334881 portion access, cell 2 achieve a 0.333089 portionaccess, cell 3 achieved a 0.328770 portion access, cell 4 achieved a0.334587 portion access and cell 5 achieved a 0.327745 portion accesswith a total convergence time of 505 seconds.

The present invention presents a frame-based, on-demand spectrumcontention protocol which is both fair and efficient. Evaluations undera simulation tool have shown that the protocol of the present inventionprovides a rapid and fair allocation of a limited resource in acognitive radio system. This allocation is on-going so as to prevent anyinterruption of data services and is further scalable to meet the needsof an expanding network.

The prior description has primarily used the example of threeoverlapping base stations in which a contention has arisen for use of ashared spectrum resources by two of three WRANs. As mentioned, theembodiments of the present invention described herein are scalable andare equally adept to complicate CR communication systems. FIG. 13 showsa series of five overlapping WRAN cells which are vying for control andaccess of a limited shared spectrum resource using one embodiment of aframe-based, on-demand spectrum contention protocol of the presentinvention.

To better understand the methodologies presented herein assume, asbefore, that a shared spectrum resource, one or more frames of asuperframe, is being occupied by Network 2 1320. Further assume that allfive WRANs depicted exist within the incumbent TV area 1360 and onlylimited portions of a single channel are available for CR use. In thisexample, Network 2 1320 is exclusively using available frames 2, 5 and 8while the incumbent utilizes frames 1, 6, 7, and 9-16. Thus, WRAN 1 1310and Network 3 1330 can, at this time, only use frames 3 or 4. If Network3 1330 is using only frame 4, Network 4 1340 is free to use frames 2, 3,5, and 8.

Network 1 1310 may experience an internal increase in demand (theaddition of more CPE in its area of responsibility) causing it to seekadditional spectrum resources. From Network 2's 1320 perspective, theinternal demand on Network 1 1310 is seen as an external demand.Accordingly, Network 1 1310, seeing that there are no unoccupied framesin the shared spectrum resource, targets at least one of frames 2, 5 or8 to meet its demand. For this example, assume Network 1 1310 istargeting frame 5.

Just as the contention protocol proceeds as previously discussed atNetwork 2 1320 with respect to frame 5, a concurrent contention can betaking place at Network 4 1340. Network 5 1350 may have initiated acontention for some of the shared spectrum resources controlled byNetwork 4 1340. For example, Network 5 may be targeting frames 4 and 5.From Network 5's 1350 perspective frame 4 is unoccupied and it can beacquired without contention.

Frame 5, however, is occupied by Network 4 1340 resulting in acontention. During the period of time governed by the length of thesuperframe in which the contention for frame 5 is decided by Network 21320, the contention for frame 5 is also determined by Network 4 1340.The superframes, during which the independent decisions are made, aresynchronized. It is possible for Network 4 1340 to lose the contentionthus releasing to Network 5 1350 control of frame 5 while at the sametime Network 2 wins the contention retaining use of frame 5. In such ascenario, Network 3 1330 is still precluded from acquiring frame 5 eventhough Network 4 1340 released frame 5. Each WRAN cell mustindependently determine its topology of one-hop neighbors and sharedspectrum resource utilization to determine which frames are availableand which are not and the distribution of occupancy of the frames canchange (and often does) upon determination interval (e.g. superframe).Over time, access to the shared spectrum is equitable.

In a preferred embodiment, the present invention can be implemented insoftware and executed on devices having a microprocessor such as acomputer, cellular telephone, personal data assistant, and the like.Software programming code which embodies the present invention istypically accessed by a microprocessor from long-term, persistentstorage media of some type, such as a flash drive or hard drive. Thesoftware programming code may be embodied on any of a variety of knownmedia for use with a data processing system, such as a diskette, harddrive, or CD-ROM. The code may be distributed on such media, or may bedistributed from the memory or storage of one computer system over anetwork of some type to other computer systems for use by such othersystems. Alternatively, the programming code may be embodied in thememory of the device and accessed by a microprocessor using an internalbus. The techniques and methods for embodying software programming codein memory, on physical media, and/or distributing software code vianetworks are well known and will not be further discussed herein.

Generally, program modules include routines, programs, objects,components, data structures and the like that perform particular tasksor implement particular abstract data types. Moreover, those skilled inthe art will appreciate that the invention can be practiced with othercomputer system configurations, including hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network PCs, minicomputers, mainframe computers and thelike. The invention may also be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotememory storage devices.

An exemplary system for implementing the invention includes a generalpurpose computing device in the form of a conventional computer, apersonal communication device or the like, including a processing unit,a system memory, and a system bus that couples various system componentsincluding the system memory to the processing unit. The system bus maybe any of several types of bus structures including a memory bus ormemory controller, a peripheral bus, and a local bus using any of avariety of bus architectures. The system memory generally includesread-only memory (ROM) and random access memory (RAM). A basicinput/output system (BIOS), containing the basic routines that help totransfer information between elements within the personal computer, suchas during start-up, is stored in ROM. The personal computer may furtherinclude a hard disk drive for reading from and writing to a hard diskand a magnetic disk drive for reading from or writing to a removablemagnetic disk. The hard disk drive and magnetic disk drive are connectedto the system bus by a hard disk drive interface and a magnetic diskdrive interface respectively. The drives and their associatedcomputer-readable media provide non-volatile storage of computerreadable instructions, data structures, program modules and other datafor the personal computer. Although the exemplary environment describedherein employs a hard disk and a removable magnetic disk, it should beappreciated by those skilled in the art that other types of computerreadable media which can store data that is accessible by a computer,such as magnetic cassettes, flash memory cards, digital video disks,random access memories (RAMs), read-only memories (ROMs) and the likemay also be used in the exemplary operating environment.

A number of program modules may be stored on the hard disk, magneticdisk, ROM or RAM, including an operating system, one or more applicationprograms or software portions, other program modules and program data. Auser may enter commands and information into the personal computerthrough input devices such as a keyboard and pointing device. Otherinput devices may include a microphone, joystick, game pad, satellitedish, scanner or the like. These and other input devices are oftenconnected to the processing unit through a serial port interface that iscoupled to the system bus, but may be connected by other interfaces,such as a parallel port, game port or universal serial bus (USB). Amonitor or other type of display device may also be connected to thesystem bus via an interface, such as a video adapter.

A computer implementing one or more embodiments of the present inventionmay operate in a networked environment using logical connections to oneor more remote computers, such as a remote computer. The remote computermay be another personal computer, a server, a router, a network PC, apeer device or other common network node, and typically includes many orall of the elements described above relative to the personal computer.The logical connections described herein include LAN and wide areanetworks (WAN). Such networking environments are commonplace in offices,enterprise-wide computer networks, Intranets and the Internet.

When used in a LAN networking environment, the personal computer isconnected to the local network through a network interface or adapter.When used in a WAN networking environment, the personal computertypically includes a means for establishing communications over the widearea network, such as the Internet. This means is connected to thesystem bus via the serial port interface. In a networked environment,program modules depicted relative to the personal computer, or portionsthereof, may be stored in the remote memory storage device. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused.

As will be understood by those familiar with the art, the invention maybe embodied in other specific forms without departing from the spirit oressential characteristics thereof. Likewise, the particular naming anddivision of the modules, managers, functions, systems, engines, layers,features, attributes, methodologies, and other aspects are not mandatoryor significant, and the mechanisms that implement the invention or itsfeatures may have different names, divisions, and/or formats.Furthermore, as will be apparent to one of ordinary skill in therelevant art, the modules, managers, functions, systems, engines,layers, features, attributes, methodologies, and other aspects of theinvention can be implemented as software, hardware, firmware, or anycombination of the three. Of course, wherever a component of the presentinvention is implemented as software, the component can be implementedas a script, as a standalone program, as part of a larger program, as aplurality of separate scripts and/or programs, as a statically ordynamically linked library, as a kernel loadable module, as a devicedriver, and/or in every and any other way known now or in the future tothose of skill in the art of computer programming. Additionally, thepresent invention is in no way limited to implementation in any specificprogramming language, or for any specific operating system orenvironment. Accordingly, the disclosure of the present invention isintended to be illustrative, but not limiting, of the scope of theinvention, which is set forth in the following claims.

While there have been described above the principles of the presentinvention in conjunction with a frame-based, on-demand spectrumcontention protocol, it is to be clearly understood that the foregoingdescription is made only by way of example and not as a limitation tothe scope of the invention. Particularly, it is recognized that theteachings of the foregoing disclosure will suggest other modificationsto those persons skilled in the relevant art. Such modifications mayinvolve other features that are already known per se and which may beused instead of or in addition to features already described herein.Although claims have been formulated in this application to particularcombinations of features, it should be understood that the scope of thedisclosure herein also includes any novel feature or any novelcombination of features disclosed either explicitly or implicitly or anygeneralization or modification thereof which would be apparent topersons skilled in the relevant art, whether or not such relates to thesame invention as presently claimed in any claim and whether or not itmitigates any or all of the same technical problems as confronted by thepresent invention. The Applicant hereby reserves the right to formulatenew claims to such features and/or combinations of such features duringthe prosecution of the present application or of any further applicationderived therefrom.

I claim:
 1. A method for use in operating a cognitive radio (CR)communication network, the method comprising: operating the CRcommunication network using synchronized frames and superframes toprovide communication services within cells of base stations of the CRcommunication network; operating a communication link between the basestations; maintaining a schedule of assignments (SchAs) of frames,within a channel, to the base stations, wherein each frame is assignedto at most one base station for exclusive use for the communicationservices by the base stations; communicating the SchAs between basestations on the communication link; and using a frame contention among aplurality of contending base stations to share use of a single channelby assigning individual frames to base stations for scheduled sole usefor communication services; wherein the frame contention comprisesmaking assignments, in the SchAs, of individual frames of subsequentsuperframes of the single channel among the plurality of contending basestations by comparing spectrum contention numbers (SCNs) which arerandomly chosen from a finite set of numbers in which each number isequally likely; and wherein the frame contention further comprises asource resolution by which a base station which does not have scheduleduse of a set of assigned frames in a subsequent superframe can contendto obtain the scheduled use of some or all of the frames in the set. 2.The method of claim 1, wherein the finite set of numbers from which SCNsare chosen is a set of integers {0, 1, . . . , 2^(X)−1}, where X is anumber of binary bits representing a fixed point integer used by the CRcommunication network.
 3. The method of claim 1, wherein thecommunication link operates using discrete sensing time periods anddiscrete messaging time periods.
 4. The method of claim 1, wherein theframe contention assigns frames from a superframe which followsimmediately after the superframe in which the frame contention occurs.5. The method of claim 1, further comprising simultaneously for eachchannel of the CR communication network, maintaining a SchAs of framesto base stations, and using the frame contention and source resolutionto share use of the channel.
 6. The method of claim 1, wherein a basestation only initiates the source resolution if the needs of the basestation for communication services exceed the communication servicesavailable in unscheduled frames of subsequent superframes.
 7. The methodof claim 1, wherein a base station initiates the source resolution by(a) identifying, from the SchAs, assigned frames to be contended for,and destination base stations to which the assigned frames to becontended for have already been assigned, (b) generating the SCNs, onefor each of the destination base stations, and (c) transmitting on thecommunication link a source request message (SC_REQ) which comprises alist of the assigned frames to be contended for, and the SCNs.
 8. Themethod of claim 7, wherein reception of the SC_REQ by destination basestations initiates, at the destination base stations to which the frameslisted in the SC_REQ have been assigned, frame contentions for theframes listed in the SC_REQ.
 9. The method of claim 7, wherein aftertransmitting the SC_REQ, the base station which initiated the sourceresolution senses on the communication link for response messages fromthe destination base stations for a fixed time.
 10. The method of claim9, wherein responsive to the base station which initiated the sourceresolution sensing one or more response messages from destination basestations, said response messages indicating either that the assignedframes contended for are maintained scheduled to the respectivedestination base station or are now available for contention, the basestation which initiated the source resolution begins a frame contentionfor frames which are now available for contention, and exits the sourceresolution.
 11. A system for a cognitive radio (CR) communicationnetwork, the system comprising: a plurality of base station transceiverseach serving as a point in a point-to-multipoint architecture,communicating on a communication link between base stations, usingsynchronized frames and superframes to provide communication serviceswithin cells of base stations, wherein there is a beacon window in eachframe; wherein the system maintains a schedule of assignments (SchAs) offrames within a channel to the base stations, wherein each frame isassigned to at most one base station for exclusive use for communicationservices by the base station; wherein the system communicates the SchAsbetween the base stations on the communication link; wherein the systemoperates a frame contention among a plurality of contending basestations to share use of a single channel by assigning frames forexclusive communication services to base stations; wherein the framecontention comprises making assignments in the SchAs of individualframes of subsequent superframes of the single channel among theplurality of contending base stations by comparing spectrum contentionnumbers (SCNs) which are randomly chosen from a finite set of numbers inwhich each number is equally likely; and wherein the frame contentionfurther comprises a source resolution by which a base station which doesnot have scheduled use of a set of assigned frames in a subsequentsuperframe can contend to obtain the scheduled use of some or all of theframes in the set.
 12. The system according to claim 11 wherein eachsuperframe includes 16 frames.
 13. The system according to claim 11,wherein the finite set of numbers from which the SCN is chosen is a setof integers {0, 1, . . . , 2^(X)−1}, where X is a number of binary bitsrepresenting a fixed point integer used by the CR communication network.14. The system according to claim 11 wherein the system is operable tosend a response message from a second base station to a first basestation with results of a frame contention and a source resolution. 15.The system according to claim 14, wherein responsive to the responsemessage indicating the first base station has won access to at least oneor more frames occupied by the second base station, the first basestation is assigned scheduled use of the at least one or more frames.16. The system of claim 11, wherein the system maintains a SchAs andoperates frame contention and source resolution simultaneously for eachchannel of the CR communication network.
 17. The system of claim 11,wherein a base station only initiates the source resolution process ifthe needs of the base station for communication services exceed thecommunication services available in unscheduled frames of subsequentsuperframes.
 18. The system of claim 11, wherein the beacon windows areused for sensing and messaging among the base stations.